1. Field of the Invention
This invention relates to a semiconductor device and a mounting structure thereof.
2. Description of the Related Art
Recently, in equipment such as personal computers and mobile devices, it has often been the case that, in order to reduce equipment size, a semiconductor device is flip-chip-mounted on a substrate. In this case, a method is employed, wherein a bare semiconductor substrate having an integrated circuit formed therein is directly provided with external electrode pads connected to the integrated circuit, and solder balls are formed on the external electrode pads, and then the solder balls are bonded to connection terminals of an external circuit board, thereby minimizing a mounting area (e.g., refer to Jpn. Pat. Appln. KOKAI Publication No. 2001-196374).
In the above-mentioned semiconductor device, a silicon oxide film is formed on a silicon substrate, and a plurality of through-holes are formed in the silicon oxide film and metal layers are provided in the through-holes. Then, a thin silicon layer is formed on the silicon oxide film, and an integrated circuit including P-type and/or N-type MOS transistors is formed in the silicon layer, and then an upper surface of the integrated circuit is covered with an interlayer insulating film. Subsequently, the silicon substrate is polished in its thickness direction from its lower side so that it completely removed to expose a lower surface of the silicon oxide film. Then, external electrode pad portions are formed at places corresponding to the through-holes provided in the silicon oxide film before solder balls are provided on the external electrode pad portions. In this manner, the external electrode pad portions and the solder balls are provided to correspond to one another in the metal layers connected to the integrated circuit via the through-holes.
Recently, semiconductor devices for control use driven at a high-speed clock of several gigahertz have emerged. It is necessary to supply a current of several tens of amperes from an external power source to such a semiconductor device. In this case, if the diameter of the solder balls provided on the external electrode pad portions is about 100 μm, a current of about 30 mA can only be passed to one solder ball in order to prevent the breakdown of the solder balls due to heat generation. Therefore, when a power source of a large current of several tens of amperes is required, a current passed to several thousand external electrode pad portions via several thousand solder balls converges inside.
For the purpose of, for example, face-down mounting to connection terminal portions of the external circuit board via the solder balls thus provided on a large number of external electrode pad portions, the size of the semiconductor device is significantly increased, which requires a large mounting area. Moreover, due to the large number of solder balls, a short-circuit occurs in a bonding step, and there is a great variation in the size of the solder balls, making it impossible to obtain reliability in connection.